Organic compounds comprising a cycloalkene ring substituted with one or more alkyl groups, such as for example alkylcyclopentenes, dialkylcyclopentenes, alkylcyclohexenes, dialkylcyclohexenes, trialkylcyclo-hexenes and alkylated alkenyl-cyclohexenes are desirable chemicals.
For example 1-methylcyclopentene, 1-methylcyclo-hexene, 1,2-dimethylcyclohexene, 1,2,4-trimethyl-4-isopropenyl-cyclohexene, are interesting gasoline blending components, as described for example in U.S. Pat. No. 2,402,863 and JP-A-09302359 and the article “Knocking Characteristics of Pure Hydrocarbons” by the American Petroleum Institute, ASTM Special Technical Publication No. 225, 1958, page 14.
In addition, such compounds comprising a cycloalkene ring substituted with one or more alkyl groups have application as starting component for various other organic compounds. For example, methylcyclopentene and/or methylcyclohexene can be used in for example the synthesis of various insecticides, resin intermediates and related products. If desirable, methylcyclopentene can be isomerized into cyclohexene or hydrogenated and isomerized into cyclohexane. Such a process can be useful if at a certain location less cyclohexane than desired is available.
If desirable, cyclohexane can, in turn, be converted to benzene. Also methylcyclopentene can be converted to benzene over a conventional reformer catalyst.
Processes for the preparation of e.g. alkylcycloalkene and/or dialkylcycloalkene are well known in the art.
For example, U.S. Pat. No. 2,593,446, U.S. Pat. No. 2,765,355 and JP-A-10036295 describe the preparation of methylcyclopentene by selective dehydrogenation of methylcyclopentane.
Such dehydrogenation, however, has several disadvantages. It is an endothermic reaction, which requires energy to be added to the process. Dehydrogenation must also be carried out at a low partial pressure in order to favor the production of olefins.
Furthermore, it is difficult to fully control the dehydrogenation. Therefore the dehydrogenation often generates less desirable by-products such as less desirable stereoisomers, di-olefins and benzene. Such di-olefins can cause fouling in a reactor under dehydrogenation conditions. Such fouling can result in considerable coke-formation.
The dehydrogenation of methylcyclopentane, for example, produces not only 1-methylcyclopentene, but also its stereoisomers such as 4-methylcyclopentene. As is clear from the above-mentioned article “Knocking Characteristics of Pure Hydrocarbons”, the latter is a less desirable gasoline blending component. A further disadvantage, specifically for the preparation of methylcyclopentene via dehydrogenation, is that the starting compound for such dehydrogenation, i.e. methylcyclopentane, is difficult to obtain in a relatively pure form by distillation. Methylcyclopentane is often obtained as a part of a C6 fraction of a gasoline, for example a fully hydrotreated pyrolysis gasoline, comprising also compounds such as n-hexane or cyclohexane. Methylcyclopentane has a boiling point of about 71° C., whereas for example n-hexane has a boiling point of about 69° C. The methylcyclopentane is, therefore, difficult to separate as a pure component through simple distillation from such n-hexane.
It would therefore be desirable to have an alternative process for the preparation of organic compounds comprising a cycloalkene ring substituted with one or more alkyl groups. It would further be desirable if such alternative process could be based on an exothermic reaction and would produce only a limited amount of undesirable byproducts such as benzene.
U.S. Pat. No. 4,151,214 describes a method comprising reacting an olefin with methanol and a catalytically effective amount of a metal halide selected from ZnI2, ZnBr2, and mixtures thereof at a temperature of from 190° C. to 300° C. In example 6, U.S. Pat. No. 4,151,214 describes the reaction of cyclohexene, methanol and Zinc Iodide at a temperature of 200° C. This process has, however, the disadvantage that the conversion and selectivity for the reaction are very low. The product stream in example 6 contained 77.7% unreacted cyclohexene, 6.2% methyl cyclohexenes and 3.2% dimethyl cyclohexenes.
It would be desirable to have a process for the alkylation of a cycloalkene with an oxygenate, which has a high conversion and/or selectivity.